1. Field of the Invention
This invention relates to a method of detecting cylinder pressure in an internal combustion engine and a cylinder pressure detection device for carrying out the method. More particularly, the invention relates to a method and a device for use in conjunction with the engine of an automobile or the like to detect the maximum value (Pmax) of the cylinder pressure and the crank angle at which the maximum value is reached.
2. Description of the Prior Art
Recent years have seen increasing adoption of methods for detecting cylinder pressure in internal combustion engines and using the detected values to control the operation of the engine as for example disclosed in Japanese Patent Publication No. 58(1983)-33394. Apart from this Publication, one of the various methods that have been proposed for this purpose is illustrated in FIG. 17.
As shown in FIG. 17(A), in this prior art method the output of a pressure sensor 500 fixed nearly at a cylinder combustion chamber is forwarded to a control unit 502, wherein it is applied to one input terminal of a comparator 504. A reference value from a decision unit 508, which may be a microcomputer or the like, is applied to the other terminal of the comparator 504 through a D/A converter 506. As shown in FIG. 17(B), the output of the comparator varies depending on the relationship between the waveform of the sensor output and the position of the reference value. While continuously discriminating the result of the comparison and changing the reference value accordingly, the decision unit determines from the pulse output by the comparator when the reference value has come in close proximity to the maximum output value of the sensor. The reference value at this time is deemed to approximate the pressure peak value.
However, since this conventional method uses only a single reference value for comparison with the pressure waveform, it is slow in detection speed and, particularly during high-speed engine operation, is incapable of adequately tracking the changes in cylinder pressure. Moreover, it is also less than satisfactory as regards accuracy.